1. Programming and Problem Solving
Chapter 4
Programming and Problem Solving

2. Flowcharting Flowchart
A graphical representation of processes (tasks) to be performed and the sequence to be followed in solving computational problem

3. Example 4.1 (1 of 2)
Write instructions to load two bytes (37H and 92H) in data registers REG0 and REG1. Add the bytes and store the sum in REG2.
Steps
Load the two bytes in data registers REG0 and REG1.
Add the bytes.
Save the sum in data register REG2.

4. Example 4.1 (2 of 2) Start ORG 0x20 Process REG0 EQU 0x00
MOVLW 0x37
MOVWF REG0,0
MOVLW 0x92
MOVWF REG1,0
ADDWF REG0,0
MOVWF REG2, 0
SLEEP
Process
Change the program: if the sum is larger than 50H then the result should be in REG3 AND REG2=0; OTHERWISE, the result should be in REG2 AND REG3=0;

5. What is wrong with this? ORG 0x20 REG0 EQU 0x00 REG1 EQU 0x01
COMPREG EQU 0x10
CONST EQU 0x50
MOVLW CONST
MOVWF COMPREG,0
MOVLW 0x37
MOVWF REG0,0
MOVLW 0x92
MOVWF REG1,0
ADDWF REG0,0 ;the result is in W
CPFSLT COMPREG,0
BRA WR_REG3
BRA WR_REG2
WR_REG3:
MOVWF REG3, 0
BRA DONE_PROG
WR_REG2:
MOVWF REG2, 0
DONE_PROG:
SLEEP

6. Steps in Writing and Executing Assembly Language Program
Analyze the problem.
Draw a flowchart.
Convert the flowchart in mnemonics.
Look up Hex code and assign memory addresses.
Enter the Hex code into memory of a lab training board.
Execute the program.
Debug the program if necessary.

7. Illustrative Program: Addition With Carry Check
Write instructions to load two bytes, Byte1 (F2H) and Byte2 (32H), in data registers REG0 and REG1 respectively and add the bytes.
If the sum generates a carry, clear the data register REG2; otherwise, save the sum in REG2.

8. Illustrative Program: Addition With Carry Check (1 of 2)
Write instructions to load two bytes, Byte1 (F2H) and Byte2 (32H), in data registers REG0 and REG1 respectively and add the bytes.
If the sum generates a carry, clear the data register REG2; otherwise, save the sum in REG2. 8

9. Integrated Development Environment (IDE)
Steps in using IDE
Editing – generating the source code
Assembling – Converting mnemonics into hex and binary; generates the object file
Linking – uses the object file and generates the binary code
Downloading – transfers the binary code (instructions) to the memory of the target device
Executing – perform the tasks specified by instruction codes
Simulation – Execute the program on PC (also called the simulator)
Debugging – Going through the program step-by-step to find logical problems in the instruction set

10. Writing a Program Using an Assembler
The assembly language program includes:
Program in mnemonics
Assembler directives
Comments

11. Assembly Language Format (1 of 2)
Typical statement of an assembly language source code has four fields:
Label
Opcode (operation code)
Operand (data, register, or memory address to be operated on)
Comment

12. Assembly Language Format (2 of 2)
Format example
Label Opcode Operand Comment
START: MOVLW 0xF2 ;Load F2H in W
↑ ↑ ↑ ↑
Space Space Space Semicolon
Or Colon

13. Assembler Directives ORG Origin END End of assembly EQU Equate
SET Defines an assembler variable
#INCLUDE Include resources from available library
RADIX Number format
DB Define byte
DW Define word
CBLOCK Define a block of constants
ENDC End of block of constants
RES Reserve memory

14. View Registers and Source Program in MPLAB Simulator
Data bytes
Define labels and const
Starting memory address
Label

15. Format of Radixes Hexadecimal Decimal Binary ASCII 0x0F H`4F` 4F 4FH
`This stuff are interesting!`

16. Using MPLAB IDE to Write, Assemble, and Build Project (1 of 6)
Write source code using MPLAB editor.
Create a new project.
Select language tool suite.
Name your project.
Add files to assemble.
Build the project.

17. Using MPLAB IDE (2 of 6) To create a new project
Step 1: Open MPLAB IDE Select Project  Project Wizard  Select Device PIC18F452 Next

18. Using MPLAB IDE (3 of 6)
Step 2: Select a Language Toolsuite: Microchip MPASM Toolsuite Next

19. Using MPLAB IDE (4 of 6)
Step 3. Name Your Project: Illust4-4 Addition with Carry Check Browse  MyProj\Ch04  Next

20. Using MPLAB IDE (5 of 6)
Step 4: Add  Add Source Files  Next

21. Using MPLAB IDE (6 of 6)
Summary  Finish

22. Project Window

23. List of Files Generated by MPLAB Assembler

24. Understanding the List File
List file generated primarily for documentation
Includes seven columns
Memory addresses where binary code is stored
Hex code
Line numbers
Contents of source file
Labels
Opcode
Operands
Comments

25. Executing a Program Using Simulator
Steps in setting up MPLAB simulator
Select Debugger  Select tool MPLABSIM
Select Debugger  Settings  Change frequency if necessary
Select View  Watch  Add registers to observe

26. View Registers and Source Program in MPLAB Simulator

27. View Registers, Source Program, and Program Memory in MPLAB Simulator

28. Debugging a Program Single-step technique Breakpoint technique
Enables user to execute one instruction at a time and observe registers for expected results
Breakpoint technique
Enables user to execute a group of instructions at a time and observe registers for expected results
Tracing code
MPLAB can track execution of each instruction and display data which can be examined for errors

29. Single-Step Technique

30. Breakpoint Technique

31. Tracing Code

32. Assembler Directive Pseudo-code instructions
Define constants, labels, where to assemble a program, reserves memory for data
Directives do not translate to machine language  do not require memory assignment (come for free!)
Example BYTE EQU 0x02
Label BYTE is being equated to value 2Hex
Example ORG 20H
Assemble the program starting at location 20H

33. Number Representation